Copyright © 2007, European Society of Cardiology
Downregulation of smooth muscle 
-actin expression by bacterial lipopolysaccharide
Department of Medicine, The University of Chicago, Chicago, IL 60637, United States
* Corresponding author. Section of Pulmonary and Critical Care Medicine, the University of Chicago Department of Medicine, 5841 S. Maryland Ave., MC 6076, Chicago, IL 60637, United States. Tel.: +1 773 702 5198. Email address: ndulin{at}medicine.bsd.uchicago.edu
Objective: Smooth muscle 
-actin (SMA) is a cytoskeletal protein characteristic to vascular smooth muscle cells (VSMC), and it serves to facilitate cell contraction and migration. Bacterial lipopolysaccharide (LPS), a major mediator of septic shock secondary to infection, is known to directly affect VSMC. The objective of this study was to investigate the effect of LPS on the expression levels of SMA in VSMC.
Methods: This study was performed on cultured VSMC derived from human aorta, human coronary artery, or rat aorta.
Results: We show that SMA expression in VSMC, induced by endothelin-1 (ET1) or transforming growth factor-β (TGF-β), is potently inhibited by a LPS. This parallels a decreased migration of VSMC after LPS treatment. Downregulation of SMA by LPS is not a result of altered signaling of ET1 or TGF-β receptors, and it is not mediated by canonical (for LPS) mechanisms, such as production of prostaglandins or nitric oxide, or secretion of other endocrine factors. On a molecular level, downregulation of SMA expression by LPS occurs at the level of transcription, as both SMA mRNA levels and SMA promoter activity are inhibited by LPS. The SMA promoter is controlled largely by two major regulatory elements–CArG boxes activated by serum response factor (SRF), and TGF-β control elements (TCE). LPS does not affect the activity of SRF, but it potently inhibits both basal and inducible TCE activation.
Conclusion: We show for the first time that LPS attenuates SMA transcription and protein expression in VSMC likely through inhibition of a TCE element on the SMA promoter.
KEYWORDS Endotoxins; Endothelins; Gene expression; Signal transduction; Smooth muscle
Abbreviations: COX, cylcooxygenase • ET1, endothelin-1 • ERK, extracellular signal regulated protein kinase • HASMC, human aortic smooth muscle cells • HCASMC, human coronary artery smooth muscle cells • iNOS, inducible nitric oxide synthase • KLF4, Kruppel-like factor 4 • L-NAME, NG-nitro-L-arginine methyl ester • LPS, lipopolysaccharide • PKA, protein kinase A • RPA, ribonuclease protection assay • SMA, smooth muscle -actin • SRF, serum response factor • TCE, transforming growth factor β control element • TGF-β, transforming growth factor β • TLR4, toll-like receptor 4 • VSMC, vascular smooth muscle cells • WKY, Wistar–Kyoto • YY1, Yin Yang 1
Time for primary review 28 days
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